Pattern Matching

I have a string like this: String s="Cat and or dog and and cow or or or and sheep";

Expected string: String result="Cat and dog and cow or sheep";

I would like to replace patterns like "and and and..." by a single "and" (same for "or"). Similarly, if there is a pattern like "and or.." or "or and or.." in the string, I want that to be replaced with the first word in the pattern. That is, by "and" , "or" respectively.

String s="Cat and or dog"; Output: Cat and dog String s="cat or and and dog"; Output: cat or dog